A gas turbine system 1 essentially comprises one or more combustion chambers 3 (see FIG. 1) in which a fuel is burned, a turbine 5 to which the combustion exhaust gases that are hot and under pressure are ducted from the combustion chambers 3 and in which the exhaust gases perform work while cooling and expanding and thereby cause the turbine 5 to rotate, and a compressor 7 that is coupled to the turbine 5 via a shaft 15 and via which the air necessary for combustion is taken in and compressed to a higher pressure.
Hot-gas-conducting housings are employed in gas turbine systems for ducting the hot combustion exhaust gases. That applies particularly to gas turbine systems of the kind in which what are termed silo combustion chambers are used that are as a rule arranged on both sides of the turbine. FIG. 1 shows a schematic view of a gas turbine system of said type, with FIG. 1a showing a horizontal and FIG. 1b a vertical section through the system. The combustion exhaust gases 2 flow out of said silo combustion chambers 3 in a direction substantially perpendicular to the rotational axis A of the turbine 5. Arranged between the outlet 18 of the silo combustion chambers and the turbine 5 is a mixer housing 8 to which on the turbine side is joined an inner housing 9 located inside the gas turbine housing 2. The function of the inner housing 9 is to protect the surrounding components from heat and redirect the hot gases exiting the mixer housing 8 toward the turbine. On exiting the inner housing 9, which means on entering the turbine 5 of the gas turbine system 1, the combustion exhaust gases then flow substantially parallel to the rotational axis A of the turbine shaft 12.
Hot-gas-conducting housings, and in particular the described inner housings in gas turbine systems having silo combustion chambers, are thermally highly stressed components. For that reason measures are taken to cool the hot-gas-ducting surfaces of the housing. Said measures include cooling the regions particularly under stress by means of a cooling fluid that flows along the outer side of the walls of said regions in order to absorb and remove the heat transferred to the hot-gas-ducting surfaces.
An inner housing 9, as previously described, has as a rule a hot-gas-ducting housing element 100 having an inner housing hub 101. The inner housing hub 101 surrounds a protective shaft jacket 115 (FIG. 7a) which in turn surrounds the shaft 12. The surface 109 of the inner housing hub 101 facing the housing interior therein forms the guiding and conducting surface for the combustion exhaust gases 2, while the surface 104 of the inner housing hub 101 facing away from the housing interior surrounds the protective shaft jacket 115. The inner housing hub 101 is fixed in position on the protective shaft jacket 115 by means of an annular rib 103 arranged centrally in the axial direction and projecting toward the protective shaft jacket 115. The protective shaft jacket 115 itself is secured to the gas turbine housing 2 and has a stud 105 in which is located an annular groove 106 into which the annular rib 103 engages. The inner housing hub 101 and protective shaft jacket 115 are mounted in the gas turbine system jointly as a unit.
To enable a cooling fluid F to flow from one side of the rib 103 or, as the case may be, of the stud 105 to the other, the stud 105 has passage openings 107 through which the cooling fluid can flow (see FIGS. 7a and 7b).
When the hot-gas-ducting housing is operating, the rib 103 is, however, heated less than the material regions closer to the hot-gas-ducting surface 109 of the cylindrical inner housing hub 101. This results in what is termed a ferrule effect that gives rise to tensions in the material regions of the inner housing hub 101 that border the rib 103. Cracks can therefore occur in the material particularly at the locations indicated by the reference numerals 111.
To reduce the risk of a defect due to cracking, the maximum number of starts, meaning the number of starts of the gas turbine system after which an inspection for cracking or a repair is to be performed, is generally limited. Furthermore the rib was relocated to the region of the inner housing's opening on the turbine side so as to be located in a thermally less stressed region of the inner housing.